Paleontology

This is a photograph of the skeleton of Alligator prenasalis. Credit: Ghedoghedo.

Paleontology is a study of fossils.

Paleontology is a large subject due to the inclusion of fossils from the rock record, taxonomic classification of these fossils, and the occasional find of residual organic material that sometimes contains genetic material.

Def. the "[s]tudy of the forms of life existing in prehistoric or geologic times"[1] is called paleontology.

Clades from the paleontological rock record sometimes display a clade asymmetry. "(Our two cases of Metazoa and mammals represent the first filling of life's ecological "barrel" for multicellular animals, and the radiation of mammals into roles formerly occupied by dinosaurs.)"[2]

Def. "[t]he mineralized remains of an animal or plant" or "[a]ny preserved evidence of ancient life, including shells, imprints, burrows, coprolites, and organically-produced chemicals"[3] is called a fossil.

These are bryozoan fossils in an Ordovician oil shale from Estonia. Credit: Mark A. Wilson.

Invertebrate paleontology is a study of fossil invertebrate animals, those which lack a backbone. Included are magafaunas whose study doesn't require a microscope, found in various phyla. Applications include stratigraphic dating and correlation, and paleo-ecology.

At the right is an example of invertebrate paleontology, specifically bryozoan fossils in an Ordovician oil shale from Estonia.

This clock representation shows some of the major units of geological time and definitive events of Earth history. Credit: Woudloper.

At right is a geologic clock representation. It shows some of the major units of geological time and definitive events of Earth history. The Hadean eon represents the time before fossil record of life on Earth; its upper boundary is now regarded as 4.0 Ga (billion years ago).[4] Other subdivisions reflect the evolution of life; the Archean and Proterozoic are both eons, the Palaeozoic, Mesozoic and Cenozoic are eras of the Phanerozoic eon. The two million year Quaternary period, the time of recognizable humans, is too small to be visible at this scale.

The following four timelines show the geologic time scale. The first shows the entire time from the formation of the Earth to the present, but this compresses the most recent eon. Therefore the second scale shows the most recent eon with an expanded scale. The second scale compresses the most recent era, so the most recent era is expanded in the third scale. Since the Quaternary is a very short period with short epochs, it is further expanded in the fourth scale. The second, third, and fourth timelines are therefore each subsections of their preceding timeline as indicated by asterisks. The Holocene (the latest epoch) is too small to be shown clearly on the third timeline on the right, another reason for expanding the fourth scale. The Pleistocene (P) epoch. Q stands for the Quaternary period.

A group of Brancasaurus brancai is in their natural habitat together with some pycnodontiformes, Caturus and Hybodus in the far background. Credit: Joschua Knüppe.{{free media}}

In the image on the right, a group of Brancasaurus brancai are portrayed in an artists impression of their natural habitat together with some pycnodontiformes, Caturus and Hybodus in the far background.

Epipliopithecus vindobonensis (Zapfe & Hürzeler, 1957) here is a fossil primate skull (cast) from the Miocene of Slovakia on public display, Field Museum of Natural History, Chicago, Illinois, USA. Credit: James St. John.{{free media}}

The Miocene dates from 23.03 x 106 to 5.332 x 106 b2k.

"A giant goose that lived on a Mediterranean island between six and nine million years ago had wings tailored for combat."[5]

"Weighing 22 kilograms and standing perhaps 1.5 metres tall, Garganornis ballmanni might be the biggest member of the duck, goose and swan family ever to have lived. Its fossilised bones have been found at Gargano and Scontrone in central Italy – a region that, during the Miocene, consisted of islands populated by unique species."[5]

"Its wing bones are short for its size, suggesting it couldn’t fly. [The] carpometacarpus bone – equivalent to the hand bones in humans – had a rounded lump called the carpal knob, a feature present in modern birds that fight each other over territory. These include some ducks, geese and the extinct Rodrigues solitaire, the closest relative of the dodo."[5]

“It’s covered over with hard skin, so it becomes a really effective weapon. In solitaires, they certainly broke each others’ bones.”[6]

"Battles over territory are the most likely reason for Garganornis‘s fighting adaptation."[6]

"Ducks and geese that live on islands, such as the extinct moanalo of Hawaii, often evolve to be terrestrial and territorial. That’s because fresh water is often in short supply, and so they live in forests as herbivores."[5]

“You’ve got this big bird, with its wings used for fighting, that would have been incredibly aggressive and would have been able to defend its young against most predators.”[6]

"As the Earth began to cool, the tropical plants that had previously been found relatively widespread began to recede towards the equator where it was still warm. The general tropical plants began a transition to more forest like areas. The first grasses also appeared in the late Oligocene. The appearance of these grasses led to to evolution of various herbivore animals. With bodies low to the ground, animals would take advantage of the new grasses that appeared."[7]

"The Cretaceous period is the third and final period in the Mesozoic Era. It began 145.5 million years ago after the Jurassic Period and ended 65.5 million years ago, before the Paleogene Period of the Cenozoic Era."[8]

The image on the right shows a juvenile Chasmosaurus fossil seen from the side.

"The Ceratopsidae are one of the more immediately recognizable groups of dinosaurs. Characterized by sharp beaks and flamboyant horns and frills, these herbivores almost all lived in what is now Western North America right at the end of the Cretaceous period, 100 to 66 million years ago."[9]

"Chasmosaurus belonged to this group [...] The 75 million-year-old fossilized Chasmosaurus was spotted in 2010 within the Dinosaur Park Formation in Alberta, Canada. In 2013, paleontologists completely unearthed it, and this week, they have described what is undoubtedly a rare specimen."[9]

“For the first time ever, we have a complete skeleton of a baby ceratopsid.”[10]

"The adult variants are certainly distinctive, with large openings in their head ornaments earning them their appropriate name, which literally means “opening lizard.” Fully grown, they reach a size of up to 4.8 meters (16 feet) and a weight of roughly 2 tonnes (2.2 tons)."[9]

"This juvenile Chasmosaurus is an adorable 1.5 meters (4.9 feet) in length, and would have weighed less than 100 kilograms (220 pounds). It’s so young that its vertebrae had not properly fused, its limbs were not fully articulated (joined up), and it had a particularly short snout. Due to its ornamental opening being fully enclosed by a single bone, scientists have deduced it is likely a species called Chasmosaurus belli."[9]

“We've only had a few isolated bones before to give us an idea of what these animals should look like as youngsters, but we've never had anything to connect all the pieces. All you need is one specimen that ties them all together. Now we have it!”[10]

Rock strata from the Late Cretaceous epoch form the Upper Cretaceous series.

The Late Cretaceous (100.5–66 Ma) is the younger of two epochs, the other being the Early Cretaceous, into which the Cretaceous period is divided in the geologic timescale.

The second image down on the right contains a 100-million-year-old chunk of amber found in Myanmar with the head, neck, wing, tail and feet of a hatchling.

"While it looks as if the actual skin and flesh of the bird are preserved in the amber, it’s basically a very detailed impression of the animal. Studies of similar finds show the flesh has broken down into carbon – and there’s no usable DNA".[11]

"The unfortunate youngster belonged to a group of birds known as the 'opposite birds' that lived alongside the ancestors of modern birds and appear to have been more diverse and successful – until they died out with the dinosaurs 66 million years ago."[12]

"In appearance, opposite birds likely resembled modern birds, but they had a socket-and-ball joint in their shoulders where modern birds have a ball-and-socket joint – hence the name. They also had claws on their wings, and jaws and teeth rather than beaks – but at the time the hatchling lived, the ancestors of modern birds had not yet evolved beaks either."[12]

This is an example of Neophyllites antecedens showing suture marks. Credit: Günter Knittel.

"The Jurassic Period takes place after the Triassic Period and before the Cretaceous Period. This period is well known for the reign of the dinosaurs of its time and the global tropical landscape."[13]

Olenekoceras meridianum is a "typical Late Olenekian [fossil which] differs in its lithology from the same zone of Russian Island, where the Zhitkov Suite has been rec- ognized (Zakharov, 1997; Zakharov et al., 2004)."[15]

With another mass extinction Mezozoic era started. Now dinosaurs rule.

"A high diversity of terrestrial vertebrates with dinosaurs as the dominant group is strongly indicated but not much of it is yet recorded."[16]

For much of the dinosaur era, the smallest sauropods are larger than anything else in their habitat, and the largest are an order of magnitude more massive than anything else that has since walked the Earth.

"The Lower Sandbian Nemagraptus gracilis Zone comprises one of the most widespread, and easily recognizable graptolite faunas in the Ordovician System. The base of the N. gracilis Zone also marks the base of the Upper Ordovician Series".[17]

This is an image of an Eurypterus lacustris fossil, Muséum national d'histoire naturelle, Paris. Credit: FunkMonk.

Although present in the Ordovician around 460 million years ago, about 410 million years ago, the first large marine predators (eurypterids), an order of arthropods, experienced a dramatic decline and are extinct.[18]

Def. the "eon from 2,500 Ma to 541.0±1.0 Ma, the beginning of the Phanerozoic, marked by the build up of oxygen in the atmosphere and the emergence of primitive multicellular life"[20] is called the Proterozoic.

To construct an hypothesis in paleontology requires statements of generalization usually using universals. Establishing that a phenomenon has occurred may require a proof of concept. Demonstrating a change from contemporary knowledge needs a control group for comparison.